DESCRIPTION: This proposal addresses the affective dimension of pain, offering a theoretical basis for defining and quantifying it. The sensory awareness of a transient injurious event takes place against a background of co-existing central nervous system and autonomically mediated responses that closely resemble the "defense response" (DR) described by Sokolov. Identification and quantification of the DR in humans may provide a basis for assessing the affective dimension of pain. The primary goal of this five year application is to evaluate the following hypotheses: 1) Painful events, unlike similar but non painful events, elicit a DR characterized by a distinctive pattern of sympathetic and central nervous system arousal; 2) the psychophysiological components of the DR resist habituation; 3) Some aspects of the DR vary across sex and age; and 4) Individual differences exist in the DR. The secondary goal is to attempt validation of the distinction between sensory and affective subjective reports of pain. The investigators propose that response latency and associated patterns of psychophysiological response differ for affective and sensory pain reports. The tertiary goal is to extend the technology for pain measurement in the human subjects laboratory. The investigators will develop new subjective report methods, quantify individual differences via mixed effects modeling, and employ structural equation modeling to define pain related psychophysiological response patterns. The project will involve two studies, the first with 100 subjects and the second with 200. The first study contrasts psychophysiological responses associated with affective versus sensory judgments and will ascertain whether psychophysiological responses contribute differentially to the judgments. The second will determine whether painful stimuli, in contrast to non painful stimuli, elicit a pattern of subjective and physiological responses that conforms to prediction based on the DR. This work will advance current understanding of the affective dimension of pain by introducing and evaluating new theory, contributing a new approach to the measurement of pain, and by demonstrating the value of structural equation modeling for human laboratory research.